Portable backup power supply



FIG. 1 is a front perspective view of a portable backup power supply, showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines in the drawings illustrate the portions of the portable backup power supply, which form no part of the claimed design. 

CLAIM The ornamental design for a portable backup power supply, as shown and described. 